For the sake of accelerating the coding process of JPEG2000 and avoiding coding useless codes,a pre-coding Rate-distortion Optimized(RDO) rate allocation algorithm was proposed.At first,a formula for minimizing the total distortion in a limited rate was proved by analyzing the rate-distortion model of wavelet coefficient,and then a realizable algorithm was provided following the distortion minimum formula.The experiment results indicate that the proposed algorithm realizes accurate pre-coding rate control and minimizes distortion.Furthermore,it makes the encoder just encode the bytes that are needed,accelerates JPEG2000 encoding process and reduces the encoder’s memory consumption.